Abstract: In a fitting process, a first pipe made of metal and a second pipe made of metal are fitted together such that an outer wall of the first pipe and an inner wall of the second pipe are opposed to each other. In a preheating process, the pipes are heated such that temperature of a fitting surface converges at a first temperature, which is lower than melting points of the pipes. In a welding process, the second pipe is irradiated with a laser to heat the pipes such that the temperature of the fitting surface converges at a second temperature, which is equal to or higher than the melting points; a vicinity of the fitting surface is melted to produce a weld penetration part; and the pipes are joined together to form a pipe joint product. An output and irradiation time of the laser in the welding process are set, so that the second temperature becomes such a temperature that a leading end of the penetration part is located within thickness of the first pipe.

Abstract: According to a laser welding method, an inert gas injection process and welding process are performed. In the inert gas injection process, inert gas is injected into an inside of a first metal pipe; and air inside the first pipe is discharged into the outside. In the welding process, a second metal pipe is irradiated with a laser from radially outward of the second pipe; metal is melted with a penetration depth of a penetration part adjusted such that a leading end of the penetration part is located within thickness of the first pipe; and the first and second pipes are welded together along the circumferential direction to form a pipe joint product. An inner wall of the first pipe maintains its pre-welding metallic luster. An injector includes an injection nozzle, a fuel passage member, a valve member accommodated in the fuel passage member, and a driving unit driving the valve member.